Constants and Variables
by TheOutlawHadMercy
Summary: The Catalyst presents Shepard with a fourth option, one that will throw him into a different universe. Literally. [Oneshot, AU, alternate ending to ME3]


**A/N: **There's a bit of Bioshock Infinite canon that inspired this short story, and while I don't mention what it is explicitly, it could spoil part of the game's ending. And of course, now that I've mentioned it, people who haven't played Infinite will probably read this and wonder "so what's the spoiler?"

You've been warned.

* * *

"I don't understand," Shepard said, glancing around him at this piece of the Citadel he doubted anyone had seen in millennia. The Catalyst stood there, its image shifting and sparking, and watched Shepard with a flat expression.

"It is not an easy concept to explain to an organic," the Catalyst continued emotionlessly, with no trace of humor. "This universe does not exist on its own. It is not singular."

Shepard shook his head. "What you're saying is impossible—there's a parallel universe to this one? That doesn't…" He trailed off, his energy fading quickly as his wounds throbbed.

"There are an infinite number of possible universes, like this one. Each one is different, but the difference can simply be a single factor. There are always variables and constants, Shepard." The Catalyst moved forward, towards the glowing generators on the far end of the Citadel's platform. Shepard followed, limping.

"Are the Reapers a constant of every universe?" Shepard asked, his mind slowly coming to speed with the implications of what the Catalyst was telling him. Other universes, different variables. It seemed abstract, like it couldn't be real.

"No. But there are other machinations that serve the same purpose. Each universe may be different, but they all gravitate towards the same constants. In another universe, there may exist a machine similar in function to a Reaper, but of a different construction. The same can be said for people. Many things are different, but in essence a lot of them remain the same." The Catalyst gestured in front of them. "Each of these choices before you—destroy, control, synthesis—they will affect your universe here. You can decide the fate of this universe."

The Catalyst pointed towards the generator on the far right side of the platform. "If you destroy the Reapers, you will earn your peace—but it is inevitable that organics and synthetics will war with each other. Organic life will cease if there is not a mechanism to preserve it." It then gestured at the opposite generator. "Control will allow you to keep the Reapers functional, but at your command, to do as you see fit. You will sacrifice your corporeal body to do so." Finally, the Catalyst pointed towards the middle of the two generators, a large green beam of energy that pulsated and seemed to disappear into the center of the Citadel. "Synthesis will end all future conflict between organics and synthetics by marrying the two together, forever. The Reapers will have no use to function, and will become dormant. This is the only option where the future is determined."

Shepard shook his head. "But synthesis would change us into what? Would we become synthetics ourselves?"

"You will lose your 'humanity,' as you call it. What makes an organic unique from a synthetic will no longer exist. However, it is those very peculiarities that created the conflict in the first place."

Shepard evened his breathing, his mind racing. The fate of the galaxy on his shoulders, and he needed to make a decision fast before he bled out. He glanced at the pistol in his head and considered his options. The Illusive Man had been right, he could control the Reapers by using the Crucible, but he would die in the process. No longer attached to a physical body, how would he change? Would his mind truly be his own? Or would he slowly become indoctrinated, convinced that the Reapers were an inevitable development, and then become just another Catalyst for someone else to argue with?

It didn't take long for him to decide. He began limping towards the right generator, his feet slow and sluggish beneath him, blood still clotting from his wounds. He had made it halfway up the ramp when he heard the Catalyst.

"There is another option," it said, its voice flat and unwavering. Shepard turned to face it.

"Another option? If it's anything like the other two you've given me, I'm not interested." He began to turn again, but the Catalyst spoke once more.

"It is a completely different option from any of the ones I have presented you thus far." It paused, and when it spoke again, Shepard could swear he heard some kind of uncertainty. "You may merge this universe with another."

Shepard stared at the Catalyst, unsure of what he just heard. "Merge?"

The Catalyst hesitated, then continued. "We have never considered the possibility, for we have never needed it. Until now, the cycles have continued flawlessly and without interruption. But, with you, it is apparent we may no longer have the correction conclusion." A console lifted from the platform's base and came to a stop in front of the Catalyst. It looked again at Shepard. "We could merge this universe with a different one, one in which there are no Reapers, or any other mechanism like them. There exists a universe that is…an anomaly."

"What do you mean, anomaly?" Shepard asked.

"Every universe is made up of constants and variables, but occasionally there is one that is considered an anomaly. It ignores the laws followed by the other universes, and its path is not one we can predict. You yourself are an anomaly. We could not have predicted you would make it this far." The Catalyst paused. "And as with all anomalies, we must find a solution. By merging the two together, we will have 'killed two birds with one stone,' as humans say."

Shit, Shepard thought. He wasn't exactly in a physical state where he could take all the time he needed to consider his options, but he knew he couldn't move forward with choosing until he was 100% certain. And that meant listening this option out as well. "What would change?" He asked.

"It may be more appropriate to ask 'what would remain the same.'" The Catalyst answered.

"Okay. What would stay the same?"

"This…anomaly, it followed a very similar pattern to the one you inhabit now. In fact, its path is practically the same as the one this universe followed, only an event occurred early in its development that in turn changed each event that followed."

"You still haven't told me what would stay the same," Shepard said impatiently.

"The people, planets. In this anomaly, the Reapers are never created because synthetic life never rebelled against their creators. Fail-safes were enacted more surely to avoid any conflict. It is like—" The Catalyst stopped speaking abruptly, and Shepard waited a full two beats before saying anything.

"Like what?"

The Catalyst remained silent and Shepard began to wonder if something had hit the Crucible to stop it from working. He was about to turn back towards the generator when it resumed.

"Someone warned it." The Catalyst said, and Shepard paused.

"Warned who about what?"

"Someone made contact with the anomaly universe and warned them of war between synthetics and organics. Hence, they were able to avoid all conflict with them, and prevent Reapers from ever developing."

"So there are no reapers in this—this other universe?"

"Correct."

"But the people, they're all the same as they are here?"

"We are currently processing that request by comparing the live individuals from this universe to the other universe in question. Please hold," The Catalyst said, looking off into the distance. A few seconds later, it replied, "There are exactly two individuals who do not exist in this universe, but do exist in the other."

Shepard frowned. For all the talk of constants and variables, _only two_ sounded like an awfully small number. Knowing he didn't have much time left, he considered his next questions carefully.

"It has the same species, the same planets, and all of the same people as this universe, only there are two that don't exist here?"

"Correct."

"And no synthetics ever went to war with organics?"

"Correct. The species you know as Quarian never fought against the synthetics known as geth."

"Known as?"

"They may have different names in this other universe."

Shepard sighed. Different names he could deal with. There was just one more question.

"What would I have to sacrifice for this choice?" He asked, wondering what else besides his physical body and/or life he could possibly have to give up. He was willing to do either if it meant every one he knew could live in peace with no future threat of Reapers or war with synthetics. That was all that mattered to him.

"We don't—" The Catalyst faltered. "We don't understand your question."

"In order to control the Reapers, I have to give up my physical body. For synthesis and destroy, I give my life. What do I have to give to merge?"

The Catalyst didn't speak for a few moments. "There are no sacrifice requirements for this choice."

Shepard shook his head, sure he didn't hear that right. "I won't die?" He asked. He certainly felt like he was about to die.

"No. It is impossible for us to know what exactly will happen to you should you chose this, but you will not die from the process. Your wounds may continue into the other universe, however, and we cannot predict what will happen with them there."

"Okay," Shepard said, after a slight pause. "I choose merge."

The Catalyst nodded. "It will be one moment to make the final preparations. Ready yourself."

Shepard grunted, wondering just how one 'readies themselves' to merge one universe with another. This had to be a first, right? Actually, probably not, considering all the possibilities. He took a deep breath and counted to five, then let it out.

"Are you ready, Shepard?" The Catalyst asked, its voice returning to its normal, unwavering and emotionless state. Shepard laughed.

"As ready as I'll ever be," he said simply. He closed his eyes, preparing for the worst.

"Starting merge," The Catalyst intoned. Shepard felt a brief prick of pain at the back of his neck, like he'd been stung by a bee. The sensation slowly spread down his spine and out to all his limbs as the pain intensified, feeling like a thousand knife cuts. He felt like he was going to cry out in pain, but no sound left his lips. He tried to open his eyes, but they were stuck shut, and he could see red edging across the undersides of his eyelids as the pain grew. Just before he felt himself slip away, he could swear he heard the Catalyst one last time.

"Good luck, Shepard."

* * *

When the Shepard woke, his anger was partially clouded by his recalling the strange dream he'd woken from. He had been on the Citadel, although on a part of it he had never seen or heard of before, talking with some VI. No, he thought groggily as he swung his feet off the bed, it hadn't been a VI. An AI then? He'd gone to bed expecting nightmares, but had gotten some cryptic dream instead. He rubbed his eyes with his middle finger and thumb, pausing briefly to assess his physical state. No headaches, no stiffness. Good, he thought. He stood up and made his way to the bathroom.

Standing in front of the mirror, shirtless and brushing his teeth, Shepard almost didn't notice the scar on his abdomen. In fact, it took two glances for it to finally sink in. "What the hell is that?" He asked himself, mouth full of toothpaste. From right beside his belly button to the bottom left side of his rib cage was a long, ugly scar. It looked pretty average, minus the slightly black striations that overlaid it. He prodded at it gently, testing to see if any pain lingered. Satisfied it didn't, he took a few moments to stare in stupor, still wondering where the hell he could have gotten that.

Eventually, he gave up and finished his morning routine. Shepard put on his best blue and gray camouflage utilities, along with his cleanest and shiniest boots, and bloused his pants sharply. Satisfied, he picked up his datapad and walked out the door of his apartment.

He spent the walk checking information on the datapad, last minute double and triple checks, making sure he hadn't missed anything in his report. He was so absorbed in the numbers that he didn't notice the Lieutenant until he was ten feet away. Lazy, he thought to himself, but still sharp.

Lieutenant Kaidan Alenko fell into step beside him and glanced at the datapad. "Still looking it over, huh, Commander?"

Shepard sighed. "I just have to be sure." He said simply. He turned the datapad off.

Kaidan put a hand on his shoulder, stopping him. "You know you've done everything you could, right?"

Shepard held his gaze for a moment, then looked away. "Have I?" He asked softly after a moment's pause. Kaidan placed his hand on Shepard's chin and turned his face back to look at him.

"Absolutely," he said, his voice sincere. They stood there like that, just looking at each other, until Kaidan felt a blush creep out from under his collar and he dropped his hand. Shepard rubbed his chin, his thoughts askew, considering if the touch had meant anything other than just friendly compassion.

Kaidan cleared his throat. "You know, Anderson would be proud of you." He said gently, watching Shepard's face for a reaction. He saw the instantaneous hardening of his eyes, the way he set his jaw and ground his teeth.

"He shouldn't have died," Shepard said hotly, his hand falling from his chin to clench into a fist at his side. He turned heel and continued walking towards the Embassy. Kaidan hurried to catch up to his pace.

"There wasn't anything else you could have done, Shepard," he said, trying to match Shepard's stride.

"No, but there's something I can do now," Shepard growled. "Those Batarian pirates are going to regret firing on the Normandy." The fire burning behind his eyes, Shepard stormed ahead of Kaidan, bound and determined to take on the entire galaxy, alone if necessary.


End file.
